Television system



Sept. 14, 1937. R, BALLARD 2,093,395

TELEVISION SYSTEM Filed Jan. 6, 1932 mul JNVENTOR. Rand all C. E)cLLlcand= /S A TTORNE Patented Sept. 14, 193

TELEVISION SYSTEM Randall C. Ballard, Merchantville, N. J., assignorto-Radio Corporation of America, a corporation of Delaware ApplicationJanuary 6,

6 Claims.

sub-multiple of the frequency of horizontal deection of the ray.

In television systems of the character referred to, it is essential, forsatisfactory operation, that vthe frequency of vertical deection of thecathode ray remain fixed at a definite sub-multiple of the frequency ofhorizontal deection of the ray. In the various systemsproposedheretofore for this purpose, and wherein the action has been such as toprovide for about twenty frames a second, each having about 120 linesor, in other Words, wherein conditions have been such as to provide forabout 2400 picture lines a second, diiiiculty has been experienced inthe Way of maintaining the vertical deflection system in .synchronismwith the horizontal defiection system. In these systems,frequentvadjustments are necessary to maintain this synchronism. Withthe advent of present developments tending to- 25 for which purpose thenumber of picture lines per second has been greatly increased, that is,to at least 4000 lines a second, the diiculty referred to above has beenfound to be still more troublesome. This is due to the fact that atthese lvery high picture-line frequencies necessary, for example, toobtain 24 frames a second each of which has 180 picture lines, thevarious adjustments for synchronism in the systems proposed heretoforeare relatively critical and, therefore, difficult to control.

With the foregoing in mind, it is one of the objects of my invention toprovide an improved television system in which the picture-linefrequency may be as high as desired, for example, 4000 cycles, theaction being such that the frequency of vertical deflection of thecathode ray `is easily and positively maintained at a definite desiredvsub-multiple of the frequency of horir zontal deflection of the ray.

Other objects and advantages will hereinafter appear.

In accordance with my invention, a cathode ray is deflected horizontallyby electromagnetic U0 coils connected to a generator of a saw-toothcurrent wave at the horizontal-deflection fre quency, and the ray isdeflected vertically by electromagnetic coils connected to a generator rof a current Wave at the framing frequency,

"" these two frequencies providing for at least 4000 ward better detailof picture reproduction, andA 1932, Serial No. 584,943V

picture lines. The two generators are maintained in synchronism'withrespect to each other by means of a frequency divider constituted by asingle electrical circuit having at its input end an oscillatoroperating at the horizontal-deflection frequency, and developing at itsoutput end i synchronizing impulses which are supplied to and drive thegenerators. The connections and adjustments are such that the frequencyof the synchronizing impulses supplied to the verticaldeection generatorare always a definite, desired sub-multiple of the frequency of thosesupplied to the horizontal-deiection generator.

Further, in accordance with my invention, the condition of synchronismreferred to is maintained by utilizing a suitable oscillator operat` ingat the desired picture-line /frequency and which is caused to drive aseries of the so-called blocking oscillators, each of which developsimpulses at a frequency which is a definite submultiple of the frequencyof those developed by the preceding blocking oscillator.

My invention resides in the improved system and method of operation ofthe character hereinafter described and claimed.

For the purpose of illustrating my invention, an embodiment thereof isshown in thedrawing', wherein Figure 1 is a diagrammatic View of atelevision transmitting systeml embodying my invention; and

Figs. 2 and 3 are graphs illustrative of the principle of operation inFig. 1.

With reference'to Fig. l, the numeral l0 designates a cathode raytransmitting tube of the general type described in the co-pendingapplications of Vladimir K. Zworykin, bearing Serial Nos. 468,610 and574,772, and filed July 17', 1930 and November 13, 1931, respectively. Asuitable generator or deecting circuit I2 operates to cause a saw-toothcurrent Wave, at a frequency of 4320 cycles, to pass throughelectromagnetic coils Ill for delecting the cathode stream or ray I6horizontally at this frequency. A second suitable generator ordeflecting circuit I8 operates to cause a saw-tooth current Wave at afrequency of 24 cycles to pass through electromagnetic coils 20 fordeflecting the Aray vertically at this frequency. For the purpose ofdeveloping picture signals, the deecting coils i4 and 20 cause the rayto-scan a target in the form of a 'suitable photo-sensitive mosaicstructure 22, onto which is projected an image of the object, such as amoving picture film 24 interposed between a light source 26 and the tubeI0.

indicated by the line d3.

The picture signals or impulses are supplied by a connection 23 to asuitable radio transmitter 30.

The generators i2 and i8 may be of the general type described in detailin the co-pending application by Arthur W. Vance, Serial No. 544,959,filed June 17, 1931. Each of these generators, as is well known, isadjusted to have a normal frequency of operation substantially equal tothe desired frequency, and are driven or caused to lock in step at thedesired frequency by synchronizing impulses occurring at the latterfrequency.

The means for developing these synchronizing impulses at the respectivedesired frequencies will now be described. Such means is constituted bythe single electrical circuit designated generally by the referenceycharacter A. This circuit has at its input end a suitable oscillator,suchA as a dynatron oscillator 32 adjusted to operate at a frequency of4320 cycles to develop in its plate circuit a sine wave at thisfrequency.

Connected to the plate circuit of the oscillator 32 is a relaxationoscillator tube 34 having its grid and plate circuits inductivelycoupled by the transformer windings 36 and 38. The polarities of thesewindings are such that when the plate begins to draw current, the gridof the tube is made more positive and, likewise, as the plate currentdecreases, the grid potential becomes more negative. A condenser i and aresistance l2 are connected as shown in the grid circuit. In operation,when the negative potential on the grid decreases to the level indicatedby the .broken line ill in Fig. 2, whereat the grid is biased tocut-off, the plate begins to draw current. By reason of the polaritiesof the transformer windings 36 and 38, the grid potential rises rapidlytoI the point of saturation and then decreases to a. point Il@ below thecut-off level. This action is attributed to the storing up of anelectrostatic charge in the condenser 40 during the time ti, t2, so thatat the end of the impulse the negative potential on the grid is at thepoint d6 below cut-01T. The Value of the resistance i2 is suficientlyhigh to permit only a relatively gradual leakage of the negative chargeon the grid, as The capacity of the condenser 40 and the value of theresistance l2 are such that only a single impulse develops in the gridcircuit, the time ti, t3 being equal to the period for one cycle ofoperation of the oscillator 32. These Values, furthermore, are suchthat. at the time t3 the charge in the condenser l0 will have leaked offby Way of the resistance i2 to a point 50 slightly removed from thepoint 52 whereat the plate will again begin to draw current. At the timet3 the next voscillation of the oscillator 32 is effective to decreasethe negative grid potential from the point 50 to or slightly beyond thepoint 52. From the foregoing, it will be seen that single sharp impulsesare developed in the grid circuit of the tube 34 at the frequency ofoscillation of the oscillator 32.' There will, therefore, be developedin the plate circuit similar sharp impulses 5G, as indicated in Fig. 3,at this same frequency, that is, 4320 cycles. By adjusting the resistor56, the level of the impulses supplied by the oscillator 32 maybeladjusted to the point whereat each oscillation is,I effective at thetime t3 to' decrease the negative potential on the grid of the tube 34from the point to or slightly beyond the point 52. A.

tube connected and adjusted to operate in the manner just explained inconnection with, the

aooset tube 3d is commonly referred to as a blocking oscillator, andWhere this term is used in the specification and claims, it is intendedto embrace a thermionic device which, while resembling a thermionicoscillator, is permitted to oscillate only once along a sharp waveduring each operating cycle, this being due to the blocking actionprovided by the condenser l0 and the resistance d2. The theory ofoperation of a, blocking oscillator of this type is discussed in greaterdetail in the co-pending application by W. A. Tolson and J. R. Duncan,bearing Serial No. 595,484, and led Feb. 27, 1932.

A second relaxation oscillator tube 5l, which operates in the samemanner as tube 34, has its grid circuit inductively coupled to the platecircuit of the latter by the transformer winding 59. The voltageimpulses in a resistor 60, and which occur at the frequency ofoscillation of the oscillator 32, are impressed on the grid circuit oftube 5l. The resistor 60 is adjusted to bring the level of theseimpulses to a point whereat only every sixth impulse is effective at thetime t3 to start the tube 5l on a new cycle of operation. The impulsesin the resistor 02 will, therefore, occur at a frequency one-sixth thatof the frequency of the impulses in the resistor 90, that is, theimpulses in the resistor 62 will occur at the rate of 720 a second.

A third relaxation oscillator tube 0G is also connected and adjusted tooperate in the same manner as the tubes 34 and 5l. The resistor t2 isadjusted to bring the level of the impulses applied to the grid circuitof the tube tl to a point whereat every sixth impulse is effective at i"the time t3 to start the tube @il on a new cycle of operation. Theimpulses in the resistor B will, therefore, occur at the rate of asecond, and these are applied to a fourth relaxation oscillator tube 63which also operates in the same manner as the tubes 3d, 5l and Btl. Theadjustment of the resistor 66 is such that every fifth impulse in thisresistor is effective to drive the tube 69 at the time t3. There will,therefore, occur in a resistor 'l0 connected as shown across thecondenser 'l2 and the resistance lli, impulses at 24 cycles. Theimpulses at 24 cycles are amplied by a suitable tube 'i6 and appear, ina resistor 'i8 connected in the plate circuit of tube llt, as ampliednegative impulses at 24 cycles.

The impulses at 4320 cycles in the resistor 60 are supplied by aconnection 8@ to a resistor 82 connected in the grid circuit of asuitable amplifier tube 84 connected in parallel to the tube i6. Theseimpulses are amplified and appear in the resistor 718 as ampliednegative impulses at 4320 cycles. By adjusting the resistors l0 and 82,the respective levels of the synchronizing impulses at the twofrequencies may be adjusted as desired. These impulses are applied tothe generators i2 and i8 by av connection 86. The adjustment of theresistor 32 is such that the synchronizing impulses at 4320 cycles areeffective to drive the generator i2, but are not of sucient amplitude todrive the generator i8.

The supply voltages for the various tubes are taken from a supply line88.

A suitable lter circuit, comprising a condenser 90 and a resistance 92,may be connected between the supply line 88 and the common groundconnection 94.

It is proposed to transmit the synchronizing impulses at the twofrequencies, for utilization at the receiving station, by impressing thesame On the grid circuit of a suitable stage in the transmitter 30, forwhich purpose a connection 96 is shown.

From the foregoing, itwill be seen that I have provided an improvedtelevision system embodying a cathode ray tube wherein the frequency ofvertical defiection of the ray is always a definite sub-multiple of thefrequency of horizontal deflection of the ray, and that by reason of theconnections. and arrangements, synchronization can be easily andpositively maintained.

While but one embodiment;v of my invention has been disclosed, it willbe understood that various modifications within the conception of thoseskilled in the art may be adopted without departing from the spirit ofmy invention or the scope of the claims.

I claim as my invention:

Y1. InY a te1evisiontr'ansmitter of the type including a cathode raytransmitter tube and horizontal and vertical deflecting means therefor,al

generator of synchronizing impulses comprising means for producingvoltage impulsesy occurring at a rate at least equal to the frequency atwhich it is desired to produce the horizontal deflection of the cathoderay, a generator of sawtooth waves coupled to said horizontal deflectingmeans, means for applying said voltage impulses to said generator andthereby producing said horizontal deflection under the control of saidvoltage impulses, means'for deriving from said voltage impulses othervoltage impulses occurring at a frequency at which it is desired toproduce the vertical deflection, of the cathode ray and which is asub-multiple of the frequency' at which said first voltage impulsesoccur, a generator of sawtooth Waves coupled to said vertical defiectingmeans, and means for applying said other voltage impulses to saidsecond-named generator and thereby producing said vertical deflectionunder the control of said other voltage impulses.

y2. The invention according to claim l characterized in that the meansfor deriving said other voltage impulses comprises a plurality ofrelaxation oscillators of the blocking oscillator type connected incascade.

3. The method of controlling the scanning action of an electron streamin a cathode ray tube having horizontal and vertical scanning meanswhich are coupled to a generator of sawtooth Waves occurring at acomparatively high frequency and to a generator of saw-tooth Wavesoccurring at a comparatively low frequency, respectively, whichcomprises generating electrical impulses at a frequency corresponding tothe desired horizontal scanning frequency, deriving other electricalimpulses from said first impulses at a frequency which is a sub-multiplethereof to control the vertical scanning, applying said first impulsesto said first saw-tooth wave generator and applying said other .impulsesto said second saw-tooth wave generator whereby the horizontaldefiection frequency always bears a definite relation to the verticaldeflection frequency irrespective of changes in the potential supplysources associated with the system.

4. In combination, a sine wave oscillator adjusted to oscillate4 at acertain frequency, a blocking oscillator coupled to said sine waveoscillator and adjusted to produce sharp voltage impulses occurring atsaid frequency, means for supplying said voltage impulses to autilization device, means for deriving from said voltage impulses othervoltage impulses occurring at a frequency which is a sub-multiple ofsaidcertain frequency, and means for supplying said other voltage irnpulsesto a utilization device.

5. In combination,'a dynatron oscillator adjusted to oscillate at acertain frequency, a blocking oscillator coupled to said dynatronoscillator and adjusted to produce sharp voltage impulses occurring atsaid frequency, means. for supplying said voltage impulses to autilization device, means for deriving from said voltage impulses othervoltage impulses occurring at a frequency which is a sub-multiple ofsaid certain frequency, and means for supplying said other voltageimpulses t-o a utilization device.

6. In a television transmitter, the method of controlling the scanningaction of an electron stream in a cathode ray transmitter tube havinghorizontal and vertical deiiecting means therefor which are coupled to agenerator of saw-tooth waves occurring at a comparatively high frequencyand to a generator of saw-tooth waves occurring at a comparatively lowfrequency, respectively, which comprises producing voltage impulsesoccurring at a rate at least as high as the frequency at which it isdesired to produce the horizontal deflection of the cathode ray,deriving from said voltage impulses other voltage impulses occurring'ata' frequency at which it is desired to produce the horizontal deflectionof the cathode ray, applying said derived impulses to the saw-tooth wavegenerator which is coupled to said horizontal deflecting means andthereby producing said horizontal deflection under the control of saidderived impulses, deriving from said first voltage impulses othervoltage impulses occurring at a frequency at which it is desired toproduce the vertical deflections of the cathode ray and which is asub-multiple of the frequency at which the first voltage impulses occur,applying the last mentioned derived impulses to the saw-tooth wavegenerator which is coupled to said vertical deflecting means and therebyproducing said vertical deflection under the control of thelast-mentioned derived impulses.

RANDALL C. BALLARD.

